Generating three-dimensional objects

ABSTRACT

Apparatus, computer readable medium, or method to determine a layer volume change in a processed layer of powder, and distribute an additional amount of powder in a subsequent layer based on the determined layer volume change.

CROSS-REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. § 371, this application is a United StatesNational Stage Application of International Patent Application No.PCT/US2014/032379, filed on Mar. 31, 2014, the contents of which areincorporated by reference as if set forth in their entirety herein.

BACKGROUND

Additive manufacturing systems that generate three-dimensional objectson a layer-by-layer basis have been proposed as a potentially convenientway to produce three-dimensional objects. The quality of objectsproduced by such systems may vary widely depending on the type ofadditive manufacturing technology used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example of an apparatus to generatethree-dimensional objects;

FIG. 2 is a diagram of another example of an apparatus to generatethree-dimensional objects;

FIG. 3 is a diagram of an example of a layer of powder having a boundportion;

FIG. 4 is a diagram of another example of a layer of powder having abound portion;

FIG. 5 is a diagram of an example of layers of powder illustrating a newto be supplied layer with partly overlapping bound portions;

FIG. 6 is a diagram of the example of layers of powder of FIG. 5 whereinsaid new layer is supplied and bound;

FIG. 7 is a flow chart of an example method of generating athree-dimensional object; and

FIG. 8 is a flow chart of another example method of generating athree-dimensional object.

DETAILED DESCRIPTION

FIG. 1 illustrates an example apparatus 1 to generate 3D(three-dimensional) objects. The apparatus 1 includes a powderdistributor 3 to distribute powder, in layers, on top of an objectsupport 9. Powder is meant to encompass powder-based materials,particulate materials and granular materials. In yet a further examplethe powder may include semi-crystalline thermoplastic material. Onesuitable material may be Nylon 12. Another suitable material may be PA2200. Suitable powders may include powdered metal materials, powderedcomposited materials, powder ceramic materials, powdered glassmaterials, powdered resin material, powdered polymer materials, and thelike.

The apparatus 1 further includes a binder 7. In one example the binder 7includes an agent distributor to dispense at least one agent inrespective patterns onto successive layers of the powder, each patterndefining a slice of the object to be generated. Here, the apparatus 1may be a powder based 3D printing apparatus. The agent may be a fluidthat stimulates binding of the powder or that adheres to or unifies withthe powder. In another example the binder 7 includes a light source toemit light in respective patterns onto successive layers of the powder.The light source is to at least partly melt the powder to unify theparticles, and thereafter solidify the unified particles, therebybinding respective patterns of the powder layer. Here, the apparatus 1may be a laser sintering apparatus and the light source includes asuitable laser source.

The binding process may involve multiple steps. One step can be themelting of the powder and another step can be the unification andsolidification of the powder. Where binding agent is used, the bindingmay involve the agent adhering to and/or melting of the powder, andsubsequent solidification of the powder and agents. In an example atemporary application of energy such as light or heat is used to aid inheating up portions of the powder above a melting point of the powderand thereby unify. In yet another example an application of energy suchas light follows after melting the powder, for example to stimulatefurther unification or solidification. In further examples, said energyis applied to the combination of powder and agent, wherein the agent mayaid in absorbing the energy.

The binder 7 is to form a unified, solidified region from the powder,and in one example from the combination of powder and agent. In thelatter example the binder 7 is an agent distributor, whereby the agentincludes a binding agent to stimulate binding of the powder. The bindingagent can include a light absorber. In one example, the binding agent isan ink, for example including an ink-type formulation such as carbonblack. The ink may include infra-red or visible light absorber. Furtherexamples of such ink are dye based color ink and pigment based colorink. In another example the agent is an adhesive. In a further example,the at least one agent comprises modifier agents. In one example suchmodifier agent includes an inhibitor that inhibits binding of thepowder. In one example such inhibitor can be distributed next to theagent in order to enhance surface characteristics of the to-be-printedobject.

The apparatus 1 includes a powder distributor 3 to distribute powderonto an object support 9 on a layer-by-layer basis. The agentdistributor 7 distributes patterns of agent onto each powder layer asderived from data representing slices of at least one 3D object to begenerated, wherein each pattern may represent one such slice. Inoperation the agent penetrates the powder, resulting in respectivesolidified object slices in each of the layers, and ultimately, in astack of bound object slices to form at least one unified object inaccordance with data representing the object to be generated.

The apparatus 1 includes a controller 11 that is connected to differentdrive and distribution components of the apparatus 1. The controller 11may include an ASIC or another type of suitable integrated circuit typecontroller. For example, the controller 11 includes at least oneprocessor 13 and at least one computer readable medium 15. The computerreadable medium 15 includes a non-transitory, non-volatile computerreadable memory for at least temporarily storing data representingslices of at least one to-be-generated object. The processor 13 is toinstruct the drive and distribution components based on said object dataand in accordance with other process specific parameters stored on thecomputer readable medium 15.

FIG. 1 illustrates an example processed layer 17 in solid lines and asubsequent to-be-build layer 19 in dotted lines. Hereafter, a “processedlayer” 17 means a layer 17 in which the pattern of powder has been boundto form the object slice, so that the layer 17 is ready to receive asubsequent layer 19 of powder on top. The processed layer 17 includes atleast one bound portion 23 and unbound powder 21 surrounding the boundportion 23. The bound portion 23 represents an object slice of theto-be-generated object. After powder distribution, each layer 17, 19 ofpowder has a predefined, constant thickness H. However, as discussedbelow, after processing the bound portions 23 may have a smallerthickness H2 than the unbound portions 21 of the layer 17.

Prior to binding there may be a relatively large amount of gas such asair in the powder. For example on average at least approximately 15volume percent, at least approximately 25 volume percent, at leastapproximately 35 volume percent, at least approximately 45 or forexample at most approximately 50 volume percent of gas may be presentbetween unbound powder particles. Herein, the volume percent of gas ismeasured relative to the combined volume of powder particles and gasbetween these particles. In certain example printing operations, most ofthe gas is released from the bound portion 23 during the process ofmelting. Therefore, the combination of powder and agent that forms thebound portion 23 contains less gas than the corresponding powder volumeprior to binding, for example less than approximately 10 volume percent,or less than approximately 5 volume percent of gas, and similarly lessgas than unbound portions 21 of the same processed layer 17. Therefore,the volume of the bound portion 23 and the total volume of the layer 17decreases by said binding process.

Upon cooling, a pattern of the powder becomes solid and forms part ofthe three-dimensional object being generated. During the process ofmelting, at least part of the gas can be released from the meltingpowder, which may lead to a lowering of the bound portion thickness H2with respect to the initial pre-binding thickness and with respect tothe thickness H of the unbound remainder 21 of the layer 17. Forexample, the thickness H2 of the bound portion 23 within the layer 17 isat least approximately 15 percent, at least approximately 25 percent, atleast approximately 35 percent, or at least approximately 45 percent andat most approximately 50 percent less than the thickness H of theunbound powder portions 21 of the layer 17. Besides the release of gas,additional variations to the overall printed layer volume may occur dueto cooling. However, in one example the shrinking effects of cooling maybe as small compared to the shrinking effect of the explained gasrelease.

The decrease of thickness of the bound portion 23 may leave a lowersurface in the processed layer 17 in the form of a pattern, hereindefined as a cavity 27. A depth H3 of the cavity 27, as measured withrespect to a top surface of unbound portions 21 of the layer 17, may, inone example, be between approximately 15 percent, approximately 25percent, approximately 35 percent or approximately 45 percent andapproximately 50 percent of the thickness H of the initial layer 17. Inone example wherein a layer thickness H is approximately 100 microns,the cavity 27 can have a depth H3 of between approximately 15 and 50microns.

The controller 11 is set to determine a layer volume change of aprocessed layer 17, with respect to its original unbound powder volume,to be able to compensate by providing more powder in a subsequent layer19. For example, the controller 11 is set to determine a layer volumechange of a processed layer 17 to be between approximately 15 and 50percent of an initial powder volume of the bound volume 23 prior tobinding. For example the layer volume change of a layer 17 is the sameas the sum of cavity volumes in that layer 17. In different examples,the controller 11 determines the layer volume change in each processedlayer 17 in different ways. For example, the layer volume change can beestimated by one or a combination of (i) sensing a layer top surfaceprofile, (ii) calculating the volume change from the stored datarepresenting slices of at least one 3D object to be generated, and (iii)sensing or measuring agent volumes for each layer 17, 19. For example,for the above items (i) and (ii) the layer volume change can beestimated by multiplying a determined surface area of the cavity 27 witha height H3 of the cavity 27.

To compensate for any cavity 27 formed in a layer of powder, thecontroller 11 is to instruct the powder distributor 3 to distribute anadditional amount of powder in addition to the predefined or “normal”layer amount of powder 29, based on the determined layer volume changein the previous layer 17. The predefined or “normal” layer amount isbased on the average x, y and z dimensions of each layer prior toprocessing and may be constant for each layer within a single print jobor a plurality of print jobs. In contrast, the additional powder amountmay be variable because it depends each time on any previously boundportion 23 that may vary in size for each layer 17, depending of earliermentioned object data. Hence, when a subsequent powder layer 19 isdistributed on top of the processed layer 17 by the powder distributor3, the additional powder amount 27 is also distributed in the cavity 27,on top of the bound portion 23, leaving a substantially flat top surfaceof the subsequent powder layer 19.

In a further example a constant margin of powder is supplied in additionto said predefined layer amount and said additional powder amount. Forexample, the controller 11 is to instruct the powder distributor 3 toinclude in each single layer distribution a constant margin independentof, and in addition to, the estimated additional powder amount that isbased on the layer volume change. Although in another examples themargin can be set higher when the estimated additional powder amount ishigher. The margin can account for potential inaccuracies incalculations or sensor measurements or other difficult-to-predictinaccuracies in the powder distribution. The margin can be approximately10 volume percent or less, approximately 5 volume percent or less orapproximately 3 volume percent or less of a total, predefined layeramount. In another example, the margin may have the same numbers inweight percentages. In one example, this margin may be constant for eachlayer and/or may depend of certain layer volume settings or othersettings of the apparatus 1 that are generally constant over thedifferent layers in a single print job. The difference with the firstmentioned additional powder amount is that the first mentionedadditional powder amount is dependent of each individual layer volumechange, and hence of the object shape that varies over the differentlayers 17, 19 in a single print job, whereas said margin is constant ordependent of certain apparatus settings or predefined layer volumes in aprint job.

For most distributed layers where there are no calculation errors, themargin causes some redundant powder to fall from the object support 9.In one example, by applying the first mentioned additional powder amountbased on the layer volume change, said margin can be set relatively low.Hence, an advantage of distributing an additional powder amount based onan estimated layer volume change may be that powder waste per print jobcan be reduced.

FIG. 2 illustrates another example diagram of an apparatus 101 togenerate three-dimensional objects shown as a cross-section view. Theapparatus 101 includes a controller 111 to instruct various drive anddistributor components. The apparatus 101 includes a drive system 131.The drive system 131 may include different drive and transmissioncomponents. The drive system 131 may include a motor such as anelectromotor and certain transmission components such as couplers andgears. In one example the motor includes a DC motor driven by a servocontrol that in turn is actuated by the controller 111, whereas thetransmission system may include at least one linear transmissioncomponent such as a worm drive or rack. In other examples, theelectromotor can include another suitable type of rotary motor or linearmotor or a stepper motor. In other examples the drive system 131includes small electro-motors or piezo-actuator devices for precisemovements of the supports 109, 133.

The apparatus 101 includes a powder distributor 103, a powder support133, and an object support 109. The powder support 133 supports thepowder to be distributed to the object support 109. The powderdistributor 103 handles the distribution of a top layer of powder on thepowder support 133 to the object support 109.

In one example, the powder distributor 103 sweeps from a start positionabove the powder support 103, over the powder support 103 and objectsupport 109, to distribute a top layer of powder from the powder support133 to the object support 109. The powder distributor 103 may include aroller, shovel, wiper or the like to move the powder from the powdersupport 133 to the object support 109 to form a new layer of powder onthe object support 109. The drive system 131 drives the powderdistributor 103. The drive system 131 also drives the object support 109and the powder support 133. In one example the drive system 131 is tomove the powder support 133 up (U) and the object support 109 down (D).Side walls 135, 136 may surround each of the supports 133, 109,respectively, to contain the powder. In one example the side walls 135,136 are static.

The apparatus 101 further includes an agent distributor 107 that is todistribute a binding agent onto a top layer of powder on the objectsupport 109. The agent distributor 107 can be arranged to scan acrossthe object support 109. In another example the agent distributor 107includes at least one printhead. In one example the printhead may be ascanning printhead that is to scan parallel to the object support 109along a single axis or in a plane perpendicular to the object supportsurface. In another example the agent distributor 107 is a staticprinthead, for example spanning the object support surface. In otherexamples the object support 109 is moves with respect to the agentdistributor 107. The agent distributor 107 may include drop actuatorssuch as thermal resistors or piezo resistors to eject drops.

In further examples, the apparatus 101 includes a sensing unit 141. Forexample the sensing unit 141 is to read top surfaces of a top layer ofpowder and output a signal that corresponds to the measured heights ofthe top layer. The sensing unit 141 is to measure a surface profile ofthe entire layer at a given sample rate or resolution. For example, thesensing unit 141 may include one of a line-type scanner or a laser arrayand at least one light detector. In a further example the sensing unit141 is attached to the agent distributor 107. For example the sensingunit 141 measures top layer heights while the agent distributor 107scans across the top layer. For example the latter example sensing unit141 is mounted to scan processed portions of the layer 117. The sensingunit 141 is to send signals corresponding to surface heights to thecontroller 111 continuously.

The controller 111 calculates a top layer volume change based on thereceived signals and instructs the powder distributor 103 to add acorresponding additional powder amount in a subsequent layer 119. Thesignals may correspond to a top surface height profile of the processedlayer 117, from which dimensions of the cavity 127 can be derived. In anexample, the calculations or estimations of the layer volume changes areto be made between consecutive layer distributions, that is, inreal-time without interrupting the printing process.

In further examples, the apparatus 101 includes an exposure unit 143.The exposure unit 143 is to emit energy to the powder and agent to aidin at least one of melting, unifying and solidifying the powder andagent to generate a bound portion 123. The exposure unit 143 may includea light or heat source. For example the exposure unit 143 may bearranged to emit electro-magnetic energy, for example light in anon-visible or visible spectrum, for example ultraviolet or infraredlight.

FIG. 2 illustrates an example of a processed layer 117 in solid linesand a subsequent to-be-distributed layer 119 in dotted lines. Theprocessed layer 117 includes a bound portion 123 and unbound powder 121surrounding the bound portion 123. The processed layer 117 includes acavity 127 above the bound portion 123. In the illustrated example, onecavity 127 forms the layer volume change.

In another example the controller 111 is to derive the layer volumechange from data representing the portions 123 that are to be bound ineach layer, which in turn may be derived from original object data. Forexample the data representing the bound portions 123 may be stored inthe form of bitmaps or original vector based data. From the boundportion data, a thickness reduction of each bound portion 123 withrespect to the initial thickness of the layer 117 can be estimated inadvance. The resulting volume change per layer 117 can be calculated orestimated based on the expected thickness reduction (e.g. 15-50%)multiplied by the summed surface areas of the bound portions 123. Otherfactors that can be taken into account for the estimation of the volumechange per layer may include characteristics of powder particles or theagents used in the process. Layer volume changes may be estimated usinga LUT (Look-up Table) stored on the computer readable medium 113.

In one example a thickness reduction of the bound portion 123 isestimated to be between approximately 15 and approximately 50 volumepercent of an unbound layer thickness and a resulting estimated layervolume change can be calculated by multiplying the estimated or sensedthickness reduction with the surface area of the bound portion 123. Forexample, the layer thickness can be derived from the apparatus settings.For example, the surface area of the bound portion 123 can be estimatedfrom the stored data representing the respective object slide.

In another example, the apparatus 101 is to measure distributed agent,for example by detecting agent drops using appropriate detection systemsor by deriving it from the object's image data. The controller 111 is toderive the layer volume change based on the detected distributed agentamounts. In a further example, the controller 111 can estimate the layervolume change by using combinations of sensed and estimated data.

In one example, for each distribution, a height of the powder support133 can be set to sweep a desired amount of powder from the powdersupport 133 to the object support 109. For example, a step height of thepowder support 133 is set in accordance with the estimated total layeramount that includes the additional powder amount. Herein the stepheight of the powder support 133 is the change in the vertical distancebetween the powder support 133 and powder distributor 103 at each step.For example a larger step height corresponds to a larger amount ofpowder that will be supplied to the object support 109. Accordingly, thecontroller 111 is to instruct the drive system 131 to set a height ofthe powder support 133 with respect to the powder distributor 103 basedon the determined layer volume change, to add powder to fill the cavity127 in addition to the predefined layer amount.

In one example, the step height of the object support 109 is keptconstant for a particular apparatus 1 or print job. Herein the stepheight of the object support 109 is the change in the vertical distancebetween the object support 109 and powder distributor 103 in one step.The object support step height can be kept constant within a certainprint job or certain print mode but may vary between different printjobs or different print modes. In other examples the object support 109and/or powder support 133 may move continuously, and the powderdistributor 103 can be set to vary the height with respect to therespective supports 109, 133.

In another example the additional powder amount can be varied byadjusting a horizontal distance HD between a starting point of thepowder distributor 103 and the object support 109. By varying thestarting point of the powder distributor 103 a total amount of powderthat can be swept is varied. If the horizontal distance HD from whichthe powder distributor 103 starts to travel in the direction to theobject support 109 is increased, also the total amount of powderdistributed over the object support 109 is increased. Hence, in oneexample the controller 111 is to instruct the powder distributor 103 toadjust a starting distance HD to the object support 109 based on thedetermined layer volume change of the previous layer 117, to reach adesired total amount of powder.

At each layer distribution action, waste material may be created in theform of redundant powder that passes over one of the walls 136 of theobject support 109. In one example, this waste material is collected bya waste material collector (not shown) and routed to the powder support133, either manually or by the apparatus 1.

Each of FIGS. 3 and 4 illustrate an example of a single processed layer217, 317, respectively, generated by a similar type apparatus in asimilar type print mode but with different sizes of bound portions 223,323 that may correspond to different slices of the same object. In FIG.3 the bound layer 217 includes a relatively small bound portion 223. Therelatively small bound portion 223 has a first thickness T between abottom of the first layer 217 and top surface of the bound portion 223.The relatively small bound portion 223 corresponds to a relatively smallcavity 227 and a relatively small layer volume change. In one examplethe first thickness T is between approximately 15 and 50 percent lessthan the thickness of the unbound remainder of the same layer 217. Inthe example of FIG. 3 a small additional amount of powder may be addedto the predefined powder amount of the subsequent layer, in order tocompensate for the layer volume change. In FIG. 4 the bound layer 317includes relatively large agent amounts to bind the powder forming arelatively large bound portion 323. The bound portion 323 has a secondthickness T that is the same as the first thickness T of the example ofFIG. 3. The bound portion 323 of FIG. 4 has a larger surface area thanFIG. 3. Hence the bound portion 323 of FIG. 4 is larger than that ofFIG. 3. For the example of FIG. 4 a relatively large amount ofadditional powder is to be added to the predefined powder amount of thesubsequent layer to compensate for the larger layer volume change, tofill a larger cavity 327.

FIG. 5 and FIG. 6 illustrate an example of layers of powder in differentsubsequent phases. The example of FIG. 5 illustrates a first bound layer417 having a first bound portion 423A corresponding to a first objectslice, unbound powder 421 and a cavity 427. As indicated in dottedlines, a second layer 419 is to be distributed on top of the first layer417. An additional powder amount is to be included in the second layer419 to fill the cavity 427.

Hence, the second layer 419 is distributed on top of the first layer 417that includes the cavity 427 whereby powder fills the cavity 427 abovethe first bound portion 423A. When distributing the binding agent ontothe second layer 419, agent penetrates downwards into the additionalamount of powder that fills said cavity 427. Thereby the binding agentin the overlapping region A joins the first bound portion 423A andresults in a higher combined bound region 423A, 423B as compared to aneighboring non-overlapping region B in the second bound region 423B.Hence there may be more volume decrease to more gas release in theoverlapping regions A of consecutive bound portions 423A, 423B.

FIG. 6 illustrates the second layer 419 after processing. In saidoverlapping region A, the second bound region 423B of the second layermay have a lower top surface than in the non-overlapping region B. Thismay be caused by further shrinking in the overlapping region A. Hence,in the second layer 419 a deeper cavity 427B is formed. Correspondinglya depth of the cavity 427B above the overlapping region A may be morethen, for example the depth of the cavity 427B above the non-overlappingregion B of the second bound portion 423B or the depth of the firstcavity 427 of the first bound portion 423A. Hence, in one example thecontroller is to estimate the layer volume change based on boundportions 423A, 423B of two consecutive layers for adequate compensation.In yet another example the reduced thickness T1 on top of theoverlapping bound portions 423A, 423B can be detected in by a sensingunit and the controller bases an estimation on the sensed signals.

FIG. 7 illustrates an example of a method of controlling a system 1,101. The method includes distributing a first layer 17, 117, 217, 317,417 of powder (block 500). The method includes binding a pattern in thefirst layer 17, 117, 217, 317, 417 of powder (block 510). In one examplesuch binding includes melting the powder with the aid of an agentsubsequently solidifying the mix of powder and agent according to saidpattern. In another example such binding includes sintering the powder,thereby melting and solidifying the powder according to said pattern.The method includes determining a layer volume change in the first layer17, 117, 217, 317, 417 of powder (block 520). In one example, the layervolume change is the decrease in volume of the entire first layer 17,117, 217, 317, 417 as a result of degassing the bound portion 23, 123,223, 323, 423A. The method further includes distributing a subsequentlayer 19, 119, 419 of powder on top of the first layer 17, 117, 217,317, 417 while including in the subsequent layer 17, 117, 217, 317, 417and additional amount of powder based on the determined layer volumechange (block 530).

FIG. 8 illustrates another example of a method of three-dimensionalprinting. The method includes determining a layer volume change within aprocessed layer 17, 117, 217, 317, 417 of powder (block 600). The methodfurther includes at least one of (i) setting a height of a powdersupport 133 with respect to a powder distributor 103 based on thedetermined layer volume change, and (ii) adjusting a starting distanceHD of a powder distributor 103 to an object support 109, based on thedetermined layer volume change (block 610). Block 610 may be executedwhile maintaining a constant step height of the object support 9, 109.

In this disclosure, the layers that are supplied to an object support 9,109 may be relatively thin, for example approximately 250 microns orless, approximately 170 microns or less, approximately 120 microns orless, for example approximately 100 microns. For example the layerthickness may be dependent of powder particle size and/or the agentcomposition. In a further example the drive system is to move the powdersupport and/or object support correspondingly, over similar stepheights. Per this disclosure, depending of the estimated layer volumechange the step height can be adjusted over less than a micron, severalmicrons or several tens of microns, for example.

In FIG. 2 only one powder support 133 is illustrated but in otherexamples multiple powder supports 133 may be used to distribute thepowder to a single object support 109. For example at least two powdersupports 133 can be used to distribute the powder to one object support109 from at least two sides, for example from opposite sides. In otherexamples, multiple bound portions are generated in one layer, andmultiple objects can be generated in one print job. Correspondingly, thelayer volume change can be sensed or estimated based on multipleseparate cavities or bound portions, respectively, in a single layer.

As noted at the beginning of this description, the examples shown in thefigures and described above illustrate but do not limit the invention.Other examples are possible. Therefore, the foregoing description shouldnot be construed to limit the scope of the invention, which is definedin the following claims.

What is claimed is:
 1. An apparatus to generate a three-dimensionalobject, comprising a powder distributor to distribute layers of powder,wherein each layer of powder comprises a predefined amount of powderthat is determined based on average dimensions of each layer prior toprocessing, a binder to bind patterns of powder in a layer of powder,and a controller to determine a layer volume change that results fromprocessing of a single processed layer of powder, calculate anadditional amount of powder to be supplied based on the layer volumechange, and cause the powder distributor to distribute in a subsequentlayer the predefined amount of powder and the additional amount ofpowder.
 2. The apparatus of claim 1 wherein the binder is an agentdistributor to distribute a binding agent on a layer of powder.
 3. Theapparatus of claim 2 wherein the controller is to determine the layervolume change based on a measured previously distributed agent amount.4. The apparatus of claim 1 comprising a powder support, an objectsupport, and a drive system to move the powder support, wherein thecontroller is to cause the drive system to set a height of the powdersupport based on the determined layer volume change.
 5. The apparatus ofclaim 4 wherein the drive system is to move the object support and thecontroller is to instruct the drive system to maintain a constant stepheight of the object support.
 6. The apparatus of claim 1 comprising anobject support, wherein the powder distributor is to distribute powderby moving from a starting point in the direction of the object support,and the controller is to cause the powder distributor to adjust ahorizontal distance between the starting point and the object supportbased on the determined layer volume change.
 7. The apparatus of claim 1comprising a sensing unit to measure top surface heights of a top layerof powder, the controller to determine the layer volume change based onsignals provided by the sensing unit.
 8. The apparatus of claim 1wherein the controller is to estimate the layer volume change based ondata defining the pattern that is to be bound within a layer of powder.9. The apparatus of claim 8 wherein the controller is to determine alayer volume change based on two consecutive layer patterns.
 10. Theapparatus of claim 1 wherein the controller is set to determine a layervolume change of a processed layer to be between approximately 15 and 50percent of an initial powder volume of a bound volume prior to binding.11. Non-transitory non-volatile computer readable medium comprisingmachine readable instructions that cause a processor to control athree-dimensional printer to generate a three-dimensional object,wherein the instructions cause the processor to: instruct a powderdistributor to distribute layers of powder, wherein each layer of powdercomprises a predefined amount of powder that is determined based onaverage dimensions of each layer prior to processing, instruct a binderto bind patterns of powder in a layer of powder, determine a layervolume change that results from processing of a single processed layerof powder, calculate an additional amount of powder to be supplied basedon the layer volume change, and instruct a powder distributor todistribute the predefined amount of powder and the additional amount ofpowder in a subsequent layer.
 12. The computer readable medium of claim11 comprising further machine readable instructions to cause a processorto instruct a drive system to set a height of a powder support based onthe determined layer volume change.
 13. The computer readable medium ofclaim 12 comprising further machine readable instructions to cause aprocessor to instruct a drive system to maintain a constant step heightof an object support.
 14. The computer readable medium of claim 11comprising further machine readable instructions to cause a processor toinstruct a drive system to set a horizontal distance between a startingpoint of a powder distributor and an object support based on thedetermined layer volume change.
 15. A method of controlling a system todistribute powder, comprising: distributing a first layer of powder,wherein the first layer of powder comprises a predefined amount ofpowder that is determined based on average dimensions of each layerprior to processing, binding a pattern in the first layer of powder,determining a layer volume change that results from processing of thefirst processed layer of powder, calculate an additional amount ofpowder to be supplied based on the layer volume change, and distributinga subsequent layer of powder on top of the first layer, wherein thesubsequent layer of powder comprises the predefined amount of powder andthe additional amount of powder.
 16. The method of claim 15, comprisingsetting a height of a powder support based on the determined layervolume change.
 17. The method of claim 15, comprising maintaining aconstant step height of an object support.
 18. The method of claim 15,setting a horizontal distance between a starting point of a powderdistributor and an object support based on the determined layer volumechange.
 19. The method of claim 15, wherein determining the layer volumechange in the first layer of powder is based on data defining thepattern that is bound within the first layer of powder.
 20. The methodof claim 15, wherein determining the layer volume change comprisessensing a top surface height of the first layer of powder.